A. Field of the Invention
This invention relates generally to the devices for interrupting electrical currents and more specifically to contact assemblies for use in circuit breaker assemblies.
B. Description of the Related Art
In the field of circuit breakers many power vacuum interrupter contacts rely on axial magnetic fields (AMFs) to accomplish interruption of high short circuit currents. In these designs the AMF strength typically is directly proportional to the amount of current flowing through the contacts. As a result, a common failure mode for current interrupter assemblies results from the concentration of the AMFs at the center of the interrupter electrode. When the AMFs concentrate sufficiently at the center of the electrode, the vacuum arc constricts in the center of the electrode as well. The interruptor assemblies therefore fail at the current zero. However, a higher relative AMF strength is needed for smaller currents to be properly interrupted.
Accordingly, there is a need for a contact design where sufficiently large magnetic field strengths are created at lower current levels to interrupt the currents when necessary while also preventing the concentration of the AMFs in the center of the interrupter electrodes at higher current levels.
The invention meets the foregoing need by utilizing saturable magnetic materials in the interrupter assembly. In certain embodiments of the invention the saturable magnetic materials are placed in the interrupter contact body and/or electrode. Because the saturable magnetic materials exhibit a non-linear magnetic field strength in response to changes in electric current, the inclusion of saturable magnetic materials in the interrupter assembly results in the redistribution of the magnetic flux within the interrupter contact assembly appropriate for the electrical conditions being experienced within the assembly at any moment in time. In other words, unlike the prior art, the magnetic field strength in the inventive interruptor assembly responds in a non-linear relationship vis-à-vis the current flowing through the assembly.
The invention may reside in any number of forms, including an interrupter assembly comprising a contact having a center and an outer edge, the contact comprising a combination of electrically conductive material and magnetic materials, the magnetic materials arranged within the contact so that an axial magnetic field produced in the contact under relatively low current conditions has a substantially constant strength from the contact center to the contact outer edge.
The invention may also be in the form of an interruptor assembly comprising a contact having a center and an outer edge, the contact comprising a combination of electrically conductive material, a first magnetic material, and a second magnetic material, the first magnetic material located near the contact outer edge and having a high magnetic saturation point and a high magnetic permeability, the second magnetic material located near the contact center and having a low magnetic saturation point and a low magnetic permeability.
Yet another form the invention may take is an interruptor assembly comprising a contact having a center and an outer edge, the contact comprising a combination of electrically conductive material, a first magnetic material, and a second magnetic material, the first magnetic material located near the contact outer edge and having a high magnetic saturation point and a low magnetic permeability, the second magnetic material located near the contact center and having a low magnetic saturation point and a high magnetic permeability.